1. Field of Endeavor
The present disclosure relates to a medium voltage inverter control apparatus and a medium voltage inverter system using the same.
2. Background
This section provides background information related to the present disclosure which is not necessarily prior art.
Generally, in order to control a multi-soft starter starting a plurality of motors using an inverter, an operation of switching a power supply inputted into the motors from an inverter output power to a commercial power source is required. At this time, the multi-soft starter is a mechanism using a method sequentially activating a plurality of motors where an inverter output is connected to one motor, which is then accelerated at an operation speed with a frequency same as that of the commercial power source, where an input power of the motor is changed to the commercial power source and an inverter output is connected to another motor, which is then accelerated to be changed to the commercial power source.
In a medium voltage inverter system, a change between an inverter output and the commercial power source is largely implemented by a VCB (Vacuum Circuit Breaker) or a VCS (Vacuum circuit Switch), where an electric shock is applied to a motor, an inverter and the commercial power source by various causes during changing operation.
FIG. 1 is an exemplified view illustrating an operation of a multi-soft starter in a medium voltage system.
Referring to FIG. 1, in order to start a motor (M1) in a conventional medium voltage inverter system, a line (A) is connected to start a medium voltage inverter (100). That is, the line (A) is interrupted after matching a frequency of the motor (M1) to that of the commercial power source, a line (B) is connected where the commercial power source and the motor (M1) are connected. Thereafter, motors are sequentially driven up to a motor (Mn) in the same fashion. This type of system is largely used for water pump facilities, and speed of the last motor (Mn) is generally controlled by the medium voltage inverter (100).
FIG. 2 is an exemplified view illustrating an operation of power change of FIG. 1. Referring to FIG. 2, an inverter switch (SW, 110) is turned off while the motor (M) is connected to the medium voltage inverter (100) via the line (A), a grid switch (SW, 120) of line (B) is connected and the commercial power source is connected to the motor (M).
However, in a case a medium voltage motor is used, an electric shock is generated by the change of the commercial power source during operation of the multi-soft starter, making it difficult to apply the multi-soft starter method to the medium voltage motor.